Method of electrically exploring bore holes



Feb. 16, 1937. E. M DERMOTT METHOD OF ELECTRICALLY EXPLORING BORE HOLES Filed March 21 1954 2 Sheets-Sheet 1 a 1 llllllllllll If INVENTOR ATTORNEY Feb. 16, 1937. E. M DERMOTT 2,070,912

' METHOD OF ELECTRICALLY EXPLORING BORE HOLES Filed March 21, 1934 2 Sheets-Sheet 2 INVENTR. @1 5 v BY ATTORNEY.

Patented Feb. 16, 1937 METHOD OF ELECTRICALLY- EXPLORING BORE HOLES Eugene MeDermott, Dallas, Tex. ApplicationMarch 21, 1934, Serial No. 716,656

4 Claims.

This invention relates to new and useful improvements in methods of exploring bore holes in the surface of the earth and it has for its principal object to provide a method for determining electrically the characteristics of rocks and other.

sub-surface formations below the earths surface without requiring the removal of the conventional drilling equipment from the bore hole.

Ar other object of the invention is to provide a medium by which to overcome the difficulties encountered in conventional methods, which require that the drill stem and bit be removed from' the bore hole or the permanent installation in the drill stem of accessory devices such as an insulated conductor which latter interferes materially with the flow of drilling fluid. The present invention requires neither of the foregoing operations for its successful performance.

The present invention contemplates a method wherein conventional rotary drilling equipment may be used with but a few simple modifications, namely; a vertical hole through the end of the drilling bit through which is passed a small cylindrical electrode, the latter,being suspended on an insulated conducting cable which is lowered into the drill stem from the earth's surface.

Since there is at least one hole in the standard drilling bit to permit the passage of drilling fluid, the same hole may be used to pass the electrode as well as the drilling fluid provided this hole is bored verticallyin the drilling bit. If not desirable to use a vertical hole, this can be plugged in any obvious and suitable manner.

With the foregoing objects as paramount, the invention has particular referenceto its salient features of construction, arrangement-of parts and steps in the method, which will become manifest as the descriptionproceeds, taken in con-- of the drawings, l designates the standard rotary drill stem having a drill bit 2 attached to its lower 'end. The drill stem l passes through a standard rotary table 3 defined to impart rotation to the drill stem and the bit. The drill bit Continuing with a more detailed description may be lifted off the bottom of the bore hole by means of the clamp 4, shown in Figure l.

The invention is comprised primarily of an electrode 5 of copper or any other suitable conducting material and is suspended from the end of a conducting cable 6 which is completely covered with an insulating material 1, shown in Figure 2. v

- The cable 6 is passed over a pulley 8 and is wound upon a drum or reel 9 which allows it to be lowered into the bore hole Ill. The opposite end of the cable 6 is free and this free end of the cable is connected toone terminal of a battery II. The other terminalofthe battery H is connected through an ammeter l2 to a plurality of ground rods, |3 -l4, to obtain low resistance connection to the ground, a voltmeter l5, arranged as shown, is employed to measure the battery voltage.

Current will thus flow through the ground from the electrode 5 in the hole ill to the ground rods l3-|4 at the surface. ance to the flow of current will be near the electrode 5 in the hole, any change in the character of the rocks or other formations, the electrode 5 penetrates will alter the flow of current and will result in a change of current flowing through the ammeter l2. It will be understood that other As the principal resist-.

and well known' indicating devices may be the circuit including the drill stem l6 and bit II.

In this case the principal resistance to thefiow of current in the circuit is that existing between the electrode l8 and bit l1. It will be understood that the bit l1 and electrode 18 are suitably spaced apart prior to recording the readings of the ammeter I9 and voltmeter 20.

Figure 5 illustrates a further modification of the invention in which the circuit is completed by employing both the ground rods 2| and 22 as well as the drill stem 23 and bit 24. The latter is spaced apart from the electrode 25, after which the readings of ammeter 2E and voltmeter 21 are recorded.

Previous research has shown satisfactorily that a clay, for example, carrying highly mineralized water will have a lower resistance than a sand carrying fresh water. Also, a sand carryingoil or gas will have a very high resistance. As a result, the indications of the meter at the surface may be used to interpret changes in rock character in the neighborhood of the bit 2.

In practice, it may be preferred that the electrode be primarily suspended a predetermined distance-below the drill bit after the drill stem has been elevated by surface equipment a distance of the-approximate length of one section thereof. Then the drill stem and electrode may be simultaneously moved up and down in the hole, relative to the bottom thereof until observations are satisfactorily completed.

Instead of inserting a battery in the system as indicated in the drawings and as described, the battery and ammeter may be omitted and a potentiometer may be used to indicate the self voltage of the rocks in the bore hole l0. In this case, the potentiometer such as'shown in Figure 3 isinserted between the conducting cable 6 and the ground rod or drill stem |3-|4 and 1 respectively. v

Manifestly, the construction shown iscapable of some modification and such modification as is considered within the scope and meaning of the appended claims is also considered within the spirit and intent of the invention.

What is claimed is.

1. The method of electrically exploring bore holes which consists in elevating the hole boring tool a predetermined distance above the bottom of the bore hole in lowering an electrode through the rotary drill stem and through a hole in the drill bit of the hole boring mechanism, in suspending said electrode in the bore hole operatively below said drill bit and insulating the same therefrom, in electrically connecting said electrode with a battery and suitable indicating in struments and. the surface of the ground and observing the change of voltage and current by means of said indicating instruments as the position of the electrode is changed in the hole.

2. The method of electrically exploring bore holes which consists in elevating the hole boring tool a substantial distance above the bottom of the bore hole in lowering an electrode through the rotary drill stem and through a hole in the drill bit of the hole drilling mechanism and suspending said electrode in' the bore hole substantially below the drill bit and insulating said electrode from said drill bit, in electrically connecting said electrode with a source of electrical energy and suitable indicating instruments and the drill stem and observing the change of electrical characteristics by means of the said indicating instruments as the position of the electrode is changed in the hole.

3. The method of electrically exploring bore holes which consists in elevating the hole boring tool a predetermined distance above the bottom of the bore hole, in. lowering an electrode through the rotary drill stem and through a hole in the drill bit of the hole boring mechanism, in suspending said electrode in the bore hole operatively below said drill bit and insulating the same therefrom, in electricallyconnecting said electrode through suitable indicating instruments with the surface of the ground and with the drill stem, and in observing the change of electrical characteristics by means of said indicating instruments as the position of the electrode is changed in the hole.

4. The method of electrically exploring bore holes which consists in elevating the hole boring tool a substantial distance above the bottom of the bore hole, in. lowering an electrode through the rotary drill stem and through a hole in the drill bit of the hole boring mechanism, in suspending said electrode in the bore hole operatively below said drill bit and insulating the same therefrom, in electrically connecting said electrode through suitable indicating instruments and the drill stem, and in observing the change of electrical characteristics by means of the said indicating as the electrode and drill stem are simultaneously moved relative to the bottom of the bore hole. 7

EUGENE MoDERMOTT. 

